I. Technical Field
The present invention relates to systems and methods for monitoring the transitory demands for electric current from the traction batteries of an electrically-powered vehicle, and more particularly, the present invention relates to systems and methods for monitoring the transitory demands for current from the vehicle's batteries and displaying the information in a format similar to that associated with a tachometer of an internal combustion engine.
II. Discussion
In an effort to improve air quality, battery-powered "electric" vehicles are becoming increasingly common in today's automotive marketplace. These electric vehicles typically include traction batteries for supplying electric current to one or more traction motors which, in turn, provide motive power to the vehicle. Accordingly, the vehicle's ability to perform a maneuver at any given time at the direction of the vehicle operator directly depends upon the condition of the traction batteries at that time. The condition of each battery, in turn, varies upon such transitory factors as its temperature and its state of charge, as well as other long-term factors such as battery aging, polarization effects, etc. Variation in these parameters will substantively affect the manner in which each battery can supply current to the vehicle's traction motors and, hence, the manner in which the vehicle will respond to commands from its operator. Stated another way, in certain situations or under certain load conditions, the vehicle's traction batteries may be unable to meet the transitory current demands of the vehicle which, in turn, will limit the vehicle's temporal capability to perform. As such, it is desirable to have a display or meter which provides information to the vehicle driver regarding the condition of the battery while power is being drawn therefrom.
One such device is generally disclosed in U.S. Pat. No. 5,568,052, entitled "Performance Monitor for Electric Vehicle," issued on Oct. 22, 1996 to Sway-Tin. This patent is owned by the Assignee of the present application and is herein incorporated by reference. This device generally discloses a system and method for displaying to the operator of an electric vehicle an indication of his present use of available battery current so that the operator may then form a reasonable expectation as to the vehicle's further capability to perform.
However, typical vehicle drivers associate the display in the '052 patent with a tachometer in an internal combustion engine driven automobile. The needle of typical tachometers usually jumps up and reads a predetermined RPM when the internal combustion engine is turned on. This is true even though the vehicle is at a standstill. As a result the vehicle driver can tell that the vehicle is on merely by observing the tachometer needle. However, the needle as disclosed in the '052 patent reads the same value when the vehicle is turned on and at a standstill and when the vehicle is turned off. Also, because electric vehicles are typically quiet, the vehicle driver cannot audibly determine whether the vehicle is on or off. As such it is desirable to provide a display which not only indicates the power consumption of a vehicle but also indicates when the vehicle is in an on condition.
Also, electric cars are fitted with a braking mechanism which charges the traction batteries. As such, it would be desirable to provide a display which indicates any recharging due to application of the brakes. The present invention was developed in light of these drawbacks.